The present invention relates generally to silicone-in-water emulsions and, specifically, to a process for emulsifying a high viscosity silicone in water, using only nonionic surfactants, and to the emulsions obtained therefrom. In a particular aspect the present invention relates to a process for emulsifying a bi-modal silicone fluid comprising a polydimethylsiloxane having a viscosity of at least 30,000 centipoise at 25.degree. C. and a substantial amount of a volatile polydimethylsiloxane.
Aqueous emulsions of silicones, including high viscosity silicones, have been prepared by emulsion polymerization of a silicon-containing monomer (Hyde et al., U.S. Pat. No. 2,891,920; Findlay et al., U.S. Pat. No. 3,294,725; and Axon, U.S. Pat. No. 3,360,491) and by direct emulsification of a preformed silicone (Green, U.S. Pat. No. 2,702,276; Volkmann et al., U.S. Pat. No. 2,755,194 and Schneider et al., U.S. Pat. No. 4,194,988). However, these processes use one or more surfactants of the ionic type for the formation and/or stabilization of the emulsion and are therefore not suitable for use in the many applications which require the absence of anionic or cationic species in the emulsion.
Evans et al., U.S. Pat. No. 3,795,538 teach a process for emulsifying a polydiorganosiloxane fluid in water using only nonionic surfactants. However, bi-modal silicone emulsions and the necessary use of a low shear generating means coupled with low temperature control of the emulsion being sheared are not contemplated therein.
Vanderhoff et al., U.S. Pat. No. 4,177,177, teach a two-step process for emulsifying a polymer phase having a viscosity of less than about 10,000 centipoise in an aqueous medium containing at least one oil-in-water functioning emulsifier, in the presence of an additive to increase the stability of the final emulsion. However, Patentees' process is not a low shear, low temperature process that is needed to emulsify a bi-modal silicone fluid.
As disclosed in a copending application Ser. No. 718,984 for U.S. patent entitled "Substantive Skin Care Compositions Comprising a Polydimethylsiloxane", filed on even date herewith and assigned to the assignee of the present invention, and now abandoned the incorporation of a polydimethylsiloxane having a viscosity of at least 30,000 centipoise into a skin care composition increases the skin-substantivity of a skin care component formulated therein. While such high viscosity silicones can be incorporated into a nonaqueous skin care composition with the aid of a solvent therefore, their incorporation into an aqueous skin care composition has been prevented by the lack of a suitable aqueous emulsion thereof. The present invention provides those suitable aqueous emulsions.
Because of the presence of two silicones having widely differing viscosities a bi-modal silicone component presents a particularly difficult challenge to existing emulsification processes. Thus, whereas the volatile (low viscosity) silicone portion of a bi-modal silicone component is normally easily reduced to a submicron emulsion particle, the high viscosity portion thereof is not. Surprisingly, the use of suitable surfactants and less shear and low temperature rather than more shear and higher temperature, provides suitable aqueous emulsions of a bi-modal silicone fluid.